The identification of the petroleum contaminants in soil or of oil sheens on water is very important for identifying the source and extent of the contamination. Those contaminants include a wide variety of volatile organic contaminants (VOC's) such as benzene, toluene, ethylbenzene, and xylenes. However, analysis of those compounds is difficult because VOC's are rapidly volatilized; loss can amount to three orders of magnitude during sampling, transportation, storage, and analytical processes. (T. Potter and J. Bruya (1993) Analysis of Petroleum Contaminated Soil and Water, from the 8th Annual Soils Conference, Univ. Mass.).
A separate problem arises because of the need for a standard in many immunoassays used to determine the concentration of the VOC. Ideally, the response (e.g., amount of color in an ELISA method) generated due to addition of the sample with an unknown analyte concentration is compared to the response generated when a known amount of analyte (the standard) is added. VOC's in aqueous solution, however, are not good standards because their concentration changes with time due to evaporation.
In view of the foregoing, it would be highly desirable to (1) be able to perform on-site analysis in order to minimize loss of such volatile compounds by minimizing transportation and storage of the samples, and (2) be able to use non-volatile standards for calibrating the assay in order to avoid loss of the standards during transportation from their site of manufacture to the site of testing.
On-site analysis is not possible for methods such as chromatography but it is possible for immunoassay analysis. Commercially available immunoassay test kits usually use either the VOC's themselves or a petroleum product mix, such as home heating oil, as calibrators. The disadvantage of the VOC's is their volatility; the disadvantage of the petroleum product mix is that it is a highly heterogeneous mixture, with batch-to-batch variations in its composition and therefore its immunoreactivity. Additionally, even the petroleum mixes contain VOC's that will evaporate and result in a decrease of immunoreactivity with time.